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Abstract:

An inkjet printing apparatus and an inkjet printing method are provided
which can correct, with high precision, print position deviations among a
plurality of printing element arrays in each of a plurality of print
modes that use different groups of printing elements in each printing
element array. The adjustment values for the print position deviations
between the first and second printing element arrays are differentiated
between the high-speed mode and the high-quality mode. In the high-speed
mode, all printing elements in the first and second printing element
arrays are used. In the high-quality mode, a part of the printing
elements in each of the first and second printing element arrays are
used. Based on these adjustment values, the ink ejection timings of the
first and second printing element arrays are adjusted.

Claims:

1. A printing apparatus to print an image on a print medium by using a
first printing element array and a second printing element array, each
having a plurality of printing elements arrayed in a first direction to
eject ink onto the print medium, and by moving the printing element
arrays relative to the print medium in a second direction crossing the
first direction, the printing apparatus comprising: a print control unit
configured to print an image in a first print mode or a second print
mode, the first and second print modes using different range in printing
elements in the first and second printing element arrays; a first
acquisition unit configured to acquire a first adjustment value for
minimizing a first deviation in the second direction between a print
position of those printing elements in the first printing element array
that are used in the first print mode and a print position of those
printing elements in the second printing element array that are used in
the first print mode; a second acquisition unit configured to acquire a
second adjustment value for minimizing a second deviation in the second
direction between a print position of those printing elements in the
first printing element array that are used in the second print mode and a
print position of those printing elements in the second printing element
array that are used in the second print mode; a first adjustment unit
configured to, when printing an image in the first print mode, adjust the
first deviation based on the first adjustment value acquired by the first
acquisition unit; and a second adjustment unit configured to, when
printing an image in the second print mode, adjust the second deviation
based on the second adjustment value acquired by the second acquisition
unit.

2. The printing apparatus according to claim 1, wherein the position of
those printing elements in the first printing element array that are used
in the first print mode and the position of those printing elements in
the second printing element array that are used in the first print mode
match in the first direction, and wherein the position of those printing
elements in the first printing element array that are used in the second
print mode and the position of those printing elements in the second
printing element array that are used in the second print mode deviate
from each other in the first direction.

3. The printing apparatus according to claim 1, wherein, in the first
print mode, all printing elements in the first printing element array and
the second printing element array are used, and wherein, in the second
print mode, a part of the printing elements in each of the first printing
element array and the second printing element array is used.

4. The printing apparatus according to claim 1, wherein the first
adjustment unit and the second adjustment unit adjust, according to the
first adjustment value and the second adjustment value, a timing at which
the printing elements eject ink.

5. The printing apparatus according to claim 1, further comprising: a
first pattern printing unit configured to print a first pattern, the
first pattern including a reference pattern printed by those printing
elements of the first printing element array that are used in the first
print mode and a plurality of non-reference patterns printed, shifted in
the second direction, by those printing elements of the second printing
element array that are used in the first print mode; and a second pattern
printing unit configured to print a second pattern, the second pattern
including a reference pattern printed by those printing elements of the
first printing element array that are used in the second print mode and a
plurality of non-reference patterns printed, shifted in the second
direction, by those printing elements of the second printing element
array that are used in the second print mode, wherein the first
acquisition unit acquires the first adjustment value based on a printed
result of the first pattern, and wherein the second acquisition unit
acquires the second adjustment value based on a printed result of the
second pattern.

6. The printing apparatus according to claim 1, further comprising: a
first pattern printing unit configured to print a first pattern, the
first pattern including a reference pattern printed by the printing
elements of the first printing element array used in the first print mode
and a plurality of non-reference patterns printed, shifted in the second
direction, by those printing elements of the second printing element
array that are used in the first print mode; and an inclination detection
unit configured to detect inclinations in the second direction of the
first printing element array and the second printing element array,
wherein the first acquisition unit acquires the first adjustment value
based on a printed result of the first pattern, and wherein the second
acquisition unit acquires the second adjustment value based on the first
adjustment value acquired by the first acquisition unit, on the
inclinations of the first printing element array and the second printing
element array detected by the inclination detection unit and on the
positions of those printing elements in the first and second printing
element arrays that are used in the second print mode.

7. The printing apparatus according to claim 6, further comprising: a
third pattern printing unit configured to print a third pattern, the
third pattern including a reference pattern printed by printing elements
situated at one end of the first printing element array and the second
printing element array and a plurality of non-reference patterns printed,
shifted in the second direction, by printing elements situated at the
other end of the first printing element array and the second printing
element array, wherein the inclination detection unit detects, based on a
printed result of the third pattern, the inclinations in the second
direction of the first printing element array and the second printing
element array.

8. The printing apparatus according to claim 6, wherein the inclinations
are equivalent to deviations in the second direction between the printing
element at the one end of each of the printing element arrays and the
printing element at the other end.

9. The printing apparatus according to claim 1, further comprising: a
first pattern printing unit configured to print a first pattern, the
first pattern including a reference pattern printed by the printing
elements of the first printing element array used in the first print mode
and a plurality of non-reference patterns printed, shifted in the second
direction, by those printing elements of the second printing element
array that are used in the first print mode; and a third acquisition unit
configured to acquire, for each of the first printing element array and
the second printing element array, a deviation in the second direction
between a predetermined one of those printing elements used in the first
print mode and a predetermined one of those printing elements used in the
second print mode, wherein the first acquisition unit acquires the first
adjustment value based on a printed result of the first pattern, and
wherein the second acquisition unit acquires the second adjustment value
based on the first adjustment value acquired by the first acquisition
unit and on the deviation acquired by the third acquisition unit.

10. A printing method for printing a image on a print medium by using a
first printing element array and a second printing element array, each
having a plurality of printing elements arrayed in a first direction to
eject ink onto the print medium, and by moving the printing element
arrays relative to the print medium in a second direction crossing the
first direction, the printing method comprising the steps of: printing an
image in a first print mode or a second print mode, the first and second
print modes using different range in printing elements in the first and
second printing element arrays; acquiring a first adjustment value for
minimizing a first deviation in the second direction between a print
position of those printing elements in the first printing element array
that are used in the first print mode and a print position of those
printing elements in the second printing element array that are used in
the first print mode; and acquiring a second adjustment value for
minimizing a second deviation in the second direction between a print
position of those printing elements in the first printing element array
that are used in the second print mode and a print position of those
printing elements in the second printing element array that are used in
the second print mode, wherein, in the printing step, when an image is
printed in the first print mode, the first deviation is adjusted based on
the first adjustment value and, when an image is printed in the second
print mode, the second deviation is adjusted based on the second
adjustment value.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a printing apparatus and a
printing method that print an image on a print medium by using a
plurality of arrays of nozzles, each capable of ejecting ink onto the
print medium.

[0003] 2. Description of the Related Art

[0004] Generally a print head used in an inkjet printing apparatus has
arrayed therein a plurality of nozzles (printing elements), each
comprising an ink ejection opening and a liquid path to supply ink to the
opening. To allow for printing color images, a plurality of such print
heads corresponding to different color inks are used.

[0005] A serial scan type inkjet printing apparatus prints an image on a
print medium by alternating a printing scan, that ejects ink from the
ejection openings as the print head travels in a main scan direction, and
a conveying operation that conveys the print medium in a sub-scan
direction crossing the main scan direction. The print head is formed with
a nozzle array (printing element array) having a plurality of nozzles
arrayed in the sub-scan direction. For faster printing speed, a
bidirectional printing method is employed, in which the printing scan is
executed both when the print head is moved in one of two opposite
directions (forward scan) along the main scan direction and when it is
moved in the other direction (backward scan).

[0006] In an inkjet printing apparatus that prints an image by using a
plurality of nozzle arrays formed in one or more print heads, image
degradations may occur when print positions deviate among nozzle arrays.
For example, in printing a pattern of vertical blue lines extending in
the sub-scan direction, lines printed by a cyan ink nozzle array and
lines printed by a magenta ink nozzle array must be aligned to overlap
each other. If the print positions of these lines are shifted in the main
scan direction, the lines fail to align with each other, making it
impossible to print a pattern of high-quality vertical blue lines.

[0007] If image impairments are caused by such print position deviations,
an adjustment needs to be made to align the print positions in the main
scan direction among a plurality of nozzle arrays (also referred to as a
"misregistration adjustment").

[0008] As one method for such a misregistration adjustment, Japanese
Patent Laid-Open No. 2007-015261 discloses a method that determines
inclinations of the nozzle arrays (inclinations of print heads) and
misregistration adjustment values among a plurality of nozzle arrays.

[0009] However, when a plurality of printing modes are used, the print
positions may not be able to be adjusted properly among a plurality of
nozzle arrays depending on the printing mode. For example, in a printing
mode that uses all nozzles of a nozzle array to print an image and in a
printing mode that uses a part of the nozzles of the nozzle array, the
effect that the inclination of the nozzle array has on the print position
deviation differs. Even if the print position adjustment value among a
plurality of nozzle arrays is determined after the nozzle array
inclination adjustment value has been determined, as in Japanese Patent
Laid-Open No. 2007-015261, there may remain a small difference in the
inclination adjustment of a magnitude less than the adjustment resolution
between the nozzle arrays. Even a slight difference in the nozzle array
inclination may produce different effects on the print position
deviations in different printing modes. This means that the use of a
single misregistration adjustment value, which is determined considering
the inclinations of nozzle arrays as described above, may not be able to
properly adjust the print positions of nozzle arrays for different
printing modes.

SUMMARY OF THE INVENTION

[0010] The present invention provides a printing apparatus and a printing
method which, in each of a plurality of printing modes that use printing
elements at different positions in a printing element array, can highly
precisely correct print position deviations among a plurality of printing
element arrays.

[0011] In the first aspect of the invention, there is provided a printing
apparatus to print an image on a print medium by using a first printing
element array and a second printing element array, each having a
plurality of printing elements arrayed in a first direction to eject ink
onto the print medium, and by moving the printing element arrays relative
to the print medium in a second direction crossing the first direction,
the printing apparatus comprising:

[0012] a print control unit configured to print an image in a first print
mode or a second print mode, the first and second print modes using
different range in printing elements in the first and second printing
element arrays;

[0013] a first acquisition unit configured to acquire a first adjustment
value for minimizing a first deviation in the second direction between a
print position of those printing elements in the first printing element
array that are used in the first print mode and a print position of those
printing elements in the second printing element array that are used in
the first print mode;

[0014] a second acquisition unit configured to acquire a second adjustment
value for minimizing a second deviation in the second direction between a
print position of those printing elements in the first printing element
array that are used in the second print mode and a print position of
those printing elements in the second printing element array that are
used in the second print mode;

[0015] a first adjustment unit configured to, when printing an image in
the first print mode, adjust the first deviation based on the first
adjustment value acquired by the first acquisition unit; and

[0016] a second adjustment unit configured to, when printing an image in
the second print mode, adjust the second deviation based on the second
adjustment value acquired by the second acquisition unit.

[0017] In the second aspect of the present invention, there is provided a
printing method for printing a image on a print medium by using a first
printing element array and a second printing element array, each having a
plurality of printing elements arrayed in a first direction to eject ink
onto the print medium, and by moving the printing element arrays relative
to the print medium in a second direction crossing the first direction,
the printing method comprising the steps of:

[0018] printing an image in a first print mode or a second print mode, the
first and second print modes using different range in printing elements
in the first and second printing element arrays;

[0019] acquiring a first adjustment value for minimizing a first deviation
in the second direction between a print position of those printing
elements in the first printing element array that are used in the first
print mode and a print position of those printing elements in the second
printing element array that are used in the first print mode; and

[0020] acquiring a second adjustment value for minimizing a second
deviation in the second direction between a print position of those
printing elements in the first printing element array that are used in
the second print mode and a print position of those printing elements in
the second printing element array that are used in the second print mode,

[0021] wherein, in the printing step, when an image is printed in the
first print mode, the first deviation is adjusted based on the first
adjustment value and, when an image is printed in the second print mode,
the second deviation is adjusted based on the second adjustment value.

[0022] With this invention, in printing modes among which those printing
elements in printing element arrays that are activated differ, print
position deviations among printing element arrays can be corrected highly
precisely, producing highly quality printed images. When different colors
of ink are applied from different printing element arrays, satisfactory
images with no color shift can be printed.

[0023] Further features of the present invention will become apparent from
the following description of exemplary embodiments (with reference to the
attached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a perspective view showing essential portions of an
inkjet printing apparatus to which this invention is applicable;

[0025]FIG. 2 is an enlarged perspective view of essential portions of a
print head of FIG. 1, showing an example construction of the print head;

[0026]FIG. 3 is a block diagram of a control system in the printing
apparatus of FIG. 1;

[0027]FIG. 4A is a schematic view of nozzles used in a high-speed mode;
and FIG. 4B is an explanatory view of nozzles used in a high-quality
mode;

[0028]FIG. 5A is a schematic view explaining a print position deviation
among nozzle arrays in the high-speed mode; and FIG. 5B is a schematic
view showing a printed image after the misregistration adjustment has
been made;

[0029] FIG. 6A is a schematic view explaining a print position deviation
among nozzle arrays in the high-quality mode; FIG. 6B is a schematic view
of a printed image after the misregistration adjustment has been made;
and FIG. 6C is an enlarged view of essential portions of the printed
image of FIG. 6B;

[0030] FIG. 7A is a schematic diagram showing nozzles used in the
high-quality mode during a 6-pass printing operation; and FIG. 7B is a
schematic diagram showing the order in which different inks are ejected
in the high-quality mode during the 6-pass printing operation;

[0031]FIG. 8 is a flow chart showing an operation to acquire adjustment
values for the print position deviations in the high-speed mode and the
high-quality mode in a first embodiment of this invention;

[0038] Embodiments of this invention will be described by referring to the
accompanying drawings.

First Embodiment

[0039]FIG. 1 is an outline perspective view showing one example
construction of a color inkjet printing apparatus to which the present
invention is applicable.

[0040] In FIG. 1, designated 202 is an ink cartridge including an ink tank
and a print head 201. In this example four ink cartridges 202 for four
color inks (black, cyan, magenta and yellow) are used. The ink cartridge
202 comprises an ink tank containing one of black, cyan, magenta and
yellow inks and a print head 201 to eject the ink. The ink tank and the
print head 201 may be constructed as separate components and take any
desired construction other than the ink cartridge 202.

[0041] A pair of paper feed rollers 105 rotate in the directions of arrows
while gripping paper (print medium) 107 in between to supply a sheet of
paper. A paper conveying roller 103 in cooperation with an auxiliary
roller 104 grips the paper 107 and conveys it in a sub-scan direction
(first direction) of arrow Y as they rotate in the directions of arrows.
A carriage 106 is movable in a main scan direction (second direction) of
arrow X crossing the sub-scan direction (in this example, at right
angles) and has four ink cartridges 202 detachably mounted thereon. The
carriage 106, during the printing operation, travels together with the
ink cartridges 202 in the main scan direction and, during non-printing
operation or during a print head recovery operation, stands by at a home
position h shown dashed in the figure. Arrow X1 represents a forward scan
direction (also referred to as a "forward direction") and arrow X2
represents a backward scan direction (also referred to as a "backward
direction").

[0042] The carriage 106 held at the home position h before the start of
the printing operation, when it receives a print start command, begins to
move in the forward direction of arrow X1. The print head 201 of the ink
cartridge 202 ejects ink as it moves in the forward direction along with
the carriage 106, printing (or forward scan) an area on the paper 107
equal in width to a printing width of the head 201. After the forward
scan is completed, the carriage 106 moves in the backward direction of
arrow X2 to return to its home position h. Then, it again moves in the
forward direction of arrow X1 to execute the printing (forward scan).
After the previous printing scan before the next printing scan is
started, the paper conveying roller 103 rotates in the direction of arrow
to convey the paper 107 a predetermined distance in the sub-scan
direction. By alternately executing the printing scan and the conveying
of the paper 107 as described above, an image is successively printed on
the paper 107. The ink ejection from the print head 201 is controlled by
a print control unit not shown.

[0043] For a faster printing speed, a bidirectional printing method may be
employed to execute the printing not just when the carriage 106 moves in
the forward direction but also in the backward direction (backward scan).

[0044] At a position where the print head undergoes a recovery operation,
there are installed a cap adapted to cap the front face (nozzle opening
surface) of the print head and a recovery unit that introduces a negative
pressure into the interior of the cap when it caps the print head to
remove viscous ink and bubbles from within the print head. There is also
a cleaning blade by the side of the cap that wipes waste ink droplets and
dirt off the front face of the print head.

[0045]FIG. 2 is a perspective view of an example construction of the
print head 201 with only its essential portions shown.

[0046] The print head 201 is formed with an array of ejection openings 300
arranged at a predetermined pitch, the array extending in a direction
cross the main scan direction (in this example, in the sub-scan
direction). In each of liquid paths 302 connecting the ejection openings
300 and a common liquid chamber 301, there is provided an ejection energy
generating element 303 along a wall surface of the liquid path 302 for
producing an energy to eject ink. In this example, electrothermal
conversion element (heater) is used as the ejection energy generating
element 303. It is also possible to use piezoelectric element instead.
The ejection openings 300, the common liquid chamber 301, the liquid
paths 302 and the ejection energy generating elements 303 combine to form
ink ejection nozzles (printing elements).

[0047] The ejection energy generating elements (referred to simply as
"heaters") 303 and their associated circuits may be formed on a silicon
plate 308 by using the semiconductor fabrication technology. A
temperature sensor and a sub-heater not shown can also be integrally
formed on the same silicon plate 308 by a process similar to the
semiconductor fabrication process. The silicon plate 308 formed with
these electric wirings is bonded to a heat-dissipating aluminum base
plate 307. A circuit connecting portion 311 on the silicon plate 308 is
connected to a printed circuit board 309 through ultrafine wires 310. A
signal from the printing apparatus body is received through a signal
circuit 312. The liquid paths 302 and the common liquid chamber 301 are
formed by an injection-molded plastic cover 306.

[0048] The common liquid chamber 301 is connected through a joint pipe 304
and an ink filter 305 to the ink tank, so that it is supplied with ink
from the ink tank. The ink, supplied from the ink tank to the common
liquid chamber 301 where it is temporarily stored, advances into the
liquid paths 302 by capillary attraction and then in the ejection
openings 300 forms meniscuses that keep it in the liquid paths 302. When
the heater 303 is energized through an electrode not shown, it rapidly
heat the ink to form a bubble in ink over the heater, causing the ink in
the liquid path 302 to be ejected in the form of ink droplet 313 from the
ejection opening 300 as the bubble expands.

[0049]FIG. 3 is a block diagram showing a configuration of the control
system in the printing apparatus.

[0050] Designated 400 is an interface to supply a print signal to the
print control unit 500, 401 an MPU, and 402 a ROM for storing a control
program to be executed by the MPU 401. Denoted 403 is a dynamic RAM
(DRAM) to store various kinds of data (e.g., print signal and print data
to be supplied to the print head). It can also store the number of dots
to be formed and the number of times that the print head has been
renewed. Reference number 404 represents a gate array 404 to control the
supply of print data to the print head and also the data transfer among
the interface 400, the MPU 401 and the DRAM 403. Denoted 406 is a carrier
motor (CR motor) to move the carriage 106 in the main scan direction and
405 a conveying motor (LF motor) to convey the paper 107 in the sub-scan
direction. Reference numbers 407 and 408 represent motor drivers to drive
the conveying motor 405 and the carrier motor 406. In a head unit 501, a
head driver 409 drives the print head 201.

[0051] In this example, four nozzle arrays (printing element arrays)
arranged in the main scan direction eject four primary color inks--black,
cyan, magenta and yellow--to print an image on the paper 107. The nozzle
arrays each have 1,200 ejection openings 300 arrayed in the sub-scan
direction at 1,200-dpi intervals and measures 1 inch long.

[0052] The printing apparatus has two print modes to be selected by the
user according to the purpose and use of printing--"high-speed mode
(first print mode)" and "high-quality mode (second print mode)". In FIG.
4A and FIG. 4B, K, C, M and Y represent nozzle arrays to eject black,
cyan, magenta and yellow ink respectively. The "high-speed mode", as
shown in FIG. 4A, uses all the nozzles in every nozzle array while the
"high-quality mode" uses different groups of nozzles in different nozzle
arrays, as shown in FIG. 4B. So, in the "high-speed mode" the positions
of nozzles used in each of the nozzle arrays match in the sub-scan
direction and, in the "high-quality mode", they shift in the sub-scan
direction. In the "high-quality mode" since the ranges of nozzles used in
each of the nozzle arrays differ in the sub-scan direction, the order of
ink ejection of different color inks can be kept constant even during the
bidirectional printing, helping to realize a high-quality image printing.

[0053] Now, examples of "high-speed mode" and "high-quality mode" will be
explained in connection with printed position deviations, as follows.

Example of High-Speed Mode

[0054]FIG. 5A and FIG. 5B illustrate an example of how vertical lines are
printed in the high-speed mode. In this example, of the four nozzle
arrays for four color inks, a cyan ink nozzle array (first printing
element array) C and a magenta ink nozzle array (second printing element
array) M are used to form blue vertical lines in a bidirectional 2-pass
printing by using all nozzles of these arrays. It is assumed that the
nozzle arrays C and M have different inclinations with respect to the
sub-scan direction, as shown in FIG. 5A. L(C) in the figure represents
lines of cyan ink printed on the paper and L(M) represents printed lines
of magenta ink.

[0055] When a position deviation D(C, M) in FIG. 5A occurs between lines
L(C) and L(M), the printed vertical blue line is recognized as having a
color deviation. D(C) represents a position deviation in the main scan
direction of line L(C) caused by the inclination of the nozzle array C
and D(M) represents a position deviation in the main scan direction of
line L(M) caused by the inclination of the nozzle array M.

[0056]FIG. 5B shows a printed result after an adjustment has been made of
the print positions of lines L(C) and L(M) printed by the nozzle arrays C
and M to eliminate the print position deviation D(C, M) (this adjustment
is also called a "misregistration adjustment"). In this example, the
misregistration adjustment was made by controlling the ink ejection
timing so that the print positions of nozzles situated near the centers
of the nozzle arrays C, M are aligned in the main scan direction.
Although there is a difference in print width between line L(C) and line
L(M), which have the position deviations D(C) and D(M) caused by the
inclinations of the nozzle arrays C, M respectively, the printed image is
good enough so that color deviations are hardly recognizable.

Example of High-Quality Mode

[0057] FIGS. 6A, 6B and 6C illustrate an example of how vertical lines are
printed in the high-quality mode. In this example, of the four nozzle
arrays for four color inks, a cyan ink nozzle array C and a magenta ink
nozzle array M are used to form blue vertical lines on the paper in a
2-pass bidirectional printing by using an upper half of nozzles in the
cyan ink nozzle array C and a lower half of nozzles in the magenta ink
nozzle array M. It is assumed that the nozzle arrays C, M have the same
inclinations as in the case of FIG. 5A. L(C) represents a line of cyan
ink formed on the paper and L(M) represents a line of magenta ink.

[0058] In unit print areas (bands) A on the paper printed by two scans of
the print head, the order of ejection of cyan and magenta inks (or the
order of ink application) remains the same. In this example, the magenta
ink line L(M) is first printed in the forward scan, followed by the cyan
ink line L(C) being formed in the backward scan. As described above,
keeping the magenta-cyan ink ejection order unchanged for all unit print
areas in the high-quality mode allows for printing images of even higher
quality. If the ink ejection order differs between the forward scan and
the backward scans, density difference and color difference may occur in
the printed images.

[0059] If print position deviation D(C, M) of FIG. 6A occurs with lines
L(C), L(M), as in the case of FIG. 5A, the printed vertical blue line is
recognized as having color deviation. Denoted d(C) is a position
deviation in the main scan direction of line L(C) caused by the
inclination of the nozzle array C and d(M) represents a position
deviation in the main scan direction of line L(M) caused by the
inclination of the nozzle array M. These deviations d(C) and d(M) are
smaller than the aforementioned deviations D(C) and D(M) of FIG. 5A and
FIG. 5B.

[0060] FIG. 6B shows a printed result after a misregistration adjustment,
similar to the one shown in FIG. 5B, has been made of the print positions
of lines L(C), L(M) printed by the nozzle arrays C, M to eliminate the
print position deviation D(C, M). In more detail, the misregistration
adjustment was made by controlling the ink ejection timing in a way that
aligns, in the main scan direction, the print position of a nozzle
situated near the center of the nozzle array C with that of a nozzle
situated near the center of the nozzle array M. Such a misregistration
adjustment, however, has a problem that a center line O(C) of the printed
line L(C) and a center line O(M) of the printed line L(M) may deviate
from each other in the main scan direction, as shown in FIG. 6C, causing
color deviation in the printed blue vertical line. Referring to FIG. 6C,
reference symbol P denotes a position in the main scan direction of
pixels printed by nozzles situated near the centers of the nozzle arrays
C, M (misregistration adjustment position). B(C) represents a deviation
between the position P and the center line O(C) of the printed line L(C),
and B(M) represents a deviation between the position P and the center
line O(M) of the printed line L(M).

[0061] As described above, if a misregistration adjustment similar to the
one performed in the high-speed mode is made in the high-quality mode, a
color deviation may occur rendering the high-quality printing impossible.
The possible causes of color deviation include inclinations of nozzle
arrays as well as the limited use of nozzles in the high-quality mode.

Another Example of High-Quality Mode

[0062] FIG. 7A and FIG. 7B show another example of high-quality mode. In
this example, an image is formed by a bidirectional 6-pass printing using
nozzle arrays C, M, Y. As shown in FIG. 7A, the nozzle array C is
operated using one third of its nozzles on the upstream side in the print
medium conveyance direction; the nozzle array M is operated using one
third of its nozzles on the central side in the print medium conveyance
direction; and the nozzle array Y is operated using one third of its
nozzles on the downstream side in the print medium conveyance direction.
In the forward and backward scans, cyan, magenta and yellow inks are
ejected from these nozzles in a fixed ink ejection order that is kept
constant throughout all unit print areas A, as shown in FIG. 7B. This
reduces color differences among unit print areas (bands), producing an
image of higher quality.

[0063] If in such a high-quality mode the misregistration adjustment
similar to the one performed in the high-speed mode is executed as in the
case of FIGS. 6A, 6B and 6C, there is a possibility of a high-quality
image not being able to be printed.

[0064] In this embodiment, to produce images with no color deviations in
any of the print modes, different print position adjustment values are
used in different print modes.

(Setting of Adjustment Value for Each Print Mode)

[0065]FIG. 8 shows a flow chart for acquiring print position adjustment
values for a high-speed mode and for a high-quality mode.

[0066] First, from step S1 to step S3, a print position adjustment value
(misregistration adjustment value) for high-speed mode is acquired as a
first adjustment value V1 and then stored in a storage media. More
specifically, by using those nozzles that are used in high-speed mode, a
predetermined pattern (first pattern) dedicated for high-speed mode is
printed (step S1) and, from the printed result, the first adjustment
value V1 is acquired (step S2). The first adjustment value V1 is then
stored in a desired region (first storage portion) of the ROM 402 (see
FIG. 3) (step S3).

[0067] The first pattern is a combination of two overlapping patterns--a
reference pattern PA of a black ink ejected from the nozzle array K and a
non-reference pattern PB of one of other inks (see FIG. 9). The
non-reference pattern PB includes a cyan ink pattern printed by the
nozzle array C, a magenta ink pattern printed by the nozzle array M and a
yellow ink pattern printed by the nozzle array Y. The first pattern
includes a pattern formed by a non-reference pattern PB of cyan ink
overlapping the reference pattern PA, a pattern formed by a non-reference
pattern PB of magenta ink overlapping the reference pattern PA, and a
pattern formed by a non-reference pattern PB of yellow ink overlapping
the reference pattern PA. These non-reference patterns PB further include
seven patterns with different offsets. So, the seven non-reference
patterns PB are each overlapped with the reference pattern PA to form a
group of first patterns.

[0068] In this example, the reference pattern PA has a vertical length (in
the sub-scan direction) equivalent to 256 pixels and a horizontal width
(in the main scan direction) measuring about 10 mm. A set S of eight
pixels comprising a 4-pixel print segment p1 and a 4-pixel blank segment
p2 is repetitively formed in the main scan direction. The seven
non-reference patterns PB are formed in a way similar to that of the
reference pattern PA. It is noted, however, that the seven non-reference
patterns PB are laterally offset from the reference pattern PA by
different amounts, with the sets S of one non-reference pattern PB being
shifted one column laterally from the sets S of the preceding
non-reference pattern PB.

[0069] In this example, the nozzle arrays each have 1,200 nozzles formed
in the sub-scan direction at 1,200-dpi intervals. So they have a
resolution of 1,200 dpi in the sub-scan direction. Their resolution in
the main scan direction is also 1,200 dpi. In this example, the first
adjustment value V1 is acquired in units of 2,400 dpi, double the
resolution of 1,200 dpi. So, those non-reference patterns PB that have
their sets S offset one column left and right from the reference pattern
PA are shown in FIG. 9 to have an offset of +2 and an offset of -2,
respectively. Similarly, the non-reference patterns PB with their sets S
offset 2 columns left and right are designated as an offset of +4 and an
offset of -4, respectively. The non-reference patterns PB with their sets
S offset 3 columns left and right are designated as an offset of +6 and
an offset of -6, respectively. The non-reference pattern PB whose sets S
are not offset are designated as an offset of ±0.

[0070] As described above, for each of cyan, magenta and yellow ink, seven
non-reference patterns PB with different offsets, each overlapping with
the reference pattern PA, are printed as the first patterns (step S1).
Next, from the printed result of these first patterns, a first adjustment
value V1 for the high-speed mode is acquired (step S2). So, to print the
first patterns, the head unit 501 functions as a first pattern printing
unit under the control of the print control unit 500.

[0071] FIG. 10A and FIG. 10B show other examples of printed results of the
first patterns.

[0072] The first patterns are printed as follows. First, the reference
pattern PA of a reference color (black) is printed using 256 nozzles
situated near the center of the nozzle array K. Next, a non-reference
pattern PB with an offset of +6 is printed using 256 nozzles of the
nozzle array C to overlap the reference pattern PA. The 256 nozzles of
the nozzle array C are at the same positions in the sub-scan direction as
those nozzles of the nozzle array K used in printing the reference
pattern PA. Similarly, the remaining non-reference patterns PB with
different offsets are printed to overlap the reference pattern PA until a
total of seven first patterns are formed. As described later, from among
the seven first patterns, a pattern with the lowest density is selected
so that the print position deviation of the nozzle array C relative to
the nozzle array K can be obtained quantitatively. For example, the user
can determine the print density of the pattern and then enter an amount
of deviation acquired based on the determined pattern density. It is also
possible to measure the print densities of the patterns using a sensor
and, based on the result of measurements, automatically acquire the
amount of position deviation.

[0073] FIG. 10A shows an example of seven first patterns printed by the
nozzle array K and nozzle array C.

[0074] In this example, a pattern formed by combining the reference
pattern and a non-reference pattern with an offset of +2 is found to be
lowest in density or grayscale level. Since the resolution of the first
patterns in the main scan direction is 1,200 dpi, the offset "+2" is
equivalent to a print position shift of about 42 μm. The print
position adjustment between the nozzle array K and C can be made by
taking the offset of "+2" as a print position adjustment value V1(C) and
shifting the cyan ink ejection timing with respect to the black ink
ejection timing by an amount equivalent to the offset of "+2" to
eliminate the position deviation between the two nozzle arrays.

[0075] FIG. 10B shows another example of seven first patterns printed by
the nozzle array K and nozzle array C. In this example, two patterns are
found to have the lowest density--a pattern formed by a combination of
the reference pattern and a non-reference pattern with an offset of +2
and a pattern formed by a combination of the reference pattern and a
non-reference pattern with an offset of +4. In this case, the position
deviation may be taken as "+3", a median value between "+2" and "+4".
That is, the print position adjustment value V1(C) can be acquired in
units of 2,400 dpi, double the resolution of 1,200 dpi.

[0076] Similarly, from the printed result of the first patterns, the print
position adjustment values V1(M) and V1(Y) for the nozzle arrays M, Y
with respect to the nozzle array K are acquired. Therefore, the first
acquisition unit for acquiring the first adjustment value (V1) includes a
first pattern printing unit, an input unit for entering the pattern
printed result (position deviation) and an MPU 401 for calculating the
adjustment value based on the position deviation. The first adjustment
value may be acquired by sensing the surface of the print head where the
nozzle arrays are formed, using an optical sensor to determine the
positional relation among nozzle arrays. That is, the first acquisition
unit does not have to include the first pattern printing unit.

[0077] In the subsequent steps S4 to S6, the print position adjustment
value (misregistration adjustment value) for the high-quality mode is
acquired as a second adjustment value V2 and stored in the storage media.
The adjustment value V2 can be acquired in a way similar to that for the
first adjustment value V1. It is noted, however, that the second patterns
printed to acquire the adjustment value V2 are printed using those
nozzles for the high-quality mode. That is, by using the nozzles for the
high-quality mode, the similar patterns to the first patterns described
above are printed as the second patterns. Therefore, the second patterns
are intended to acquire the second adjustment value. To print the second
patterns, the head unit functions as a second pattern printing unit under
the control of the print control unit 500. The adjustment values V2(C),
V2(M), V2(Y) for the position deviations of nozzle arrays C, M, Y with
respect to the nozzle array K are stored in a predetermined region
(second storage portion) of the ROM 402 (see FIG. 3). The second
acquisition unit for the second adjustment values (V2) includes a second
pattern printing unit, an input unit for entering the pattern printed
result (position deviation) and an MPU 401 for calculating the adjustment
value based on the position deviation. It is noted that the second
acquisition unit does not have to include the second pattern printing
unit.

[0078] As described above, this embodiment prints in each print mode
predetermined patterns using those nozzles assigned for the selected mode
and, based on the printed results, position deviation adjustment values
are acquired. This allows an optimal adjustment value to be used in the
print position deviation adjustment to prevent possible color deviations
even in cases where, in such a print mode as a high-speed mode in which
the number and positions of the nozzles used differ among different
nozzle arrays, there are variations in inclination among different print
heads.

[0079] The first and second patterns described above are just one example
and the resolution may be raised further to enhance the precision of
detection of the inclinations of nozzle arrays. It is also possible to
increase the detection range of inclination by extending the horizontal
size of the patterns or increasing the number (or kinds) of non-reference
patterns. In cases where the number of nozzles used in each nozzle array
is fewer than 256, there may arise a need to change patterns according to
a variety of print conditions, as by reducing the vertical size of the
first and second patterns. Furthermore, the processing shown in FIG. 8 to
determine the print position adjustment values in the main scan direction
may be executed after acquiring the inclination adjustment values for the
nozzle arrays K, C, M, Y and correcting the inclinations of the nozzle
arrays based on the inclination adjustment values. That is, even after
the nozzle array inclination adjustment has been made, an inclination
mismatch of a magnitude less than the inclination adjustment resolution
may remain. So, the same effect as the one described above can be
produced by determining the main scan direction registration adjustment
value in each of the print modes with different ranges of the nozzles
used.

Second Embodiment

[0080] FIG. 11 is a flow chart showing the method of acquiring the print
position adjustment values for the high-speed mode and the high-quality
mode, respectively.

[0081] First, at step S11, print position adjustment values (first
adjustment values) V1 for all nozzle arrays with respect to one reference
nozzle array are acquired. In this example, the nozzle array K is taken
as the reference nozzle array, and the print position adjustment values
V1(C), V1(M), V1(Y) for the nozzle arrays C, M, Y with respect to the
reference nozzle array K are acquired.

[0082] The method of acquiring these adjustment values is similar to step
S1 and S2 of FIG. 8. These adjustment values are stored in a
predetermined area (first storage portion) in the ROM 402 (see FIG. 3) as
by input from the user (step S12).

[0083] Next, the number n of nozzle arrays, which is initially set at "0",
is counted up (step S13). The nozzle array number represents the total
number of nozzle arrays, which is four in this example. Then, an
inclination S of an n-th nozzle array with respect to the sub-scan
direction is acquired (step S14).

[0084] The inclination S of the nozzle array in this example will be
explained below.

[0085] FIG. 12 shows a nozzle array L being rotated about a middle point
of its length in a plane defined by an axis extending in the main scan
direction (main scan axis), Ox, and an axis extending in the sub-scan
direction (sub-scan axis), Oy. In FIG. 12, an uppermost nozzle NT of the
nozzle array L is projected onto the axis Ox and its projected point on
the axis Ox is designated X(T). A point on the axis Ox at which a
lowermost nozzle NB of the nozzle array L is projected to the axis Ox is
designated X(B). The axis Ox has a zero point where it crosses the axis
Oy at right angles. On the right side of the zero point in the FIG. 12
the axis Ox takes positive values while on the left side it takes
negative values. In this example, a value X(T)-X(B) is defined as the
inclination S of the nozzle array L. If the nozzle array L is not
inclined, as shown by a one-dot chain line in FIG. 12, S=0. If the nozzle
array L is inclined, S≠0. Depending on whether S takes a negative
value (S<0) or a positive value (S>0), the direction of inclination
of the nozzle array L (direction of rotation) can be determined.

[0086] FIG. 13 shows an example of patterns printed on a print medium to
acquire the inclination S of the nozzle array L. The patterns are a
combination of a reference pattern P1 and non-reference patterns P2.

[0087] Each of the patterns P1, P2 has a length equivalent to 256 pixels
in a vertical direction (sub-scan direction), a width of 8 pixels in a
horizontal direction (main scan direction) and a resolution of 1,200 dpi
in both vertical and horizontal directions. The reference pattern P1 is
used to print a 2-pixel-wide vertical line consisting of two vertically
extending 256-pixel dot columns (fourth and fifth columns from the left
end of the pattern made up of eight vertical columns arranged side by
side in the horizontal direction). The non-reference pattern P2, similar
to the reference pattern P1, is also used to print a 2-pixel wide
vertical line consisting of two vertically extending 256-pixel dot
columns. It is noted, however, that there are seven different
non-reference patterns P2. The position of the printed vertical line
shifts one pixel to the right from the left end of the pattern each time
the vertical line is printed by one of the non-reference patterns P2
after another. In this example, because the inclination S is acquired in
units of 2,400 dpi, two times the printing resolution of 1,200 dpi, the
seven non-reference patterns P2 are matched to inclinations of +6, +4,
+2, ±0, -2, -4 and -6, respectively.

[0088] The reference pattern P1 is printed by using a bottom group of 256
nozzles arranged continuously upward from the lowermost nozzle NB of
1,200 nozzles in the nozzle array L (one-end nozzle group). Then, after a
print medium is fed in the sub-scan direction by a distance equal to the
length of the nozzle array L (in this case, 1 inch), a non-reference
pattern P2 that matches an inclination of +6 is printed by using a top
group of 256 nozzles arranged continuously downward from the uppermost
nozzle NT (other-end nozzle group). This process is repeated until seven
vertical line patterns, each a combination of the reference pattern P1
and one of the non-reference patterns P2, are printed as shown in FIG.
14A or FIG. 14B. These vertical line patterns can be printed separated
from each other at a predetermined interval. The user then checks the
seven vertical line patterns and selects one in which the reference
pattern P1 and the non-reference pattern P2 are connected in a straight
line. The inclination corresponding to the non-reference pattern P2 of
the selected vertical line pattern is then acquired as the inclination S
of the nozzle array L.

[0089] FIG. 14A shows a printed result of patterns when the nozzle array L
has almost no inclination S, with a non-reference pattern P2, that
matches the inclination of ±0, connecting with the reference pattern
P1 in a straight line. If the nozzle array L is inclined, a non-reference
pattern P2 other than the one matching the inclination of ±0 connects
with the reference pattern P1 in a straight line, as shown in FIG. 14B.
In the case of FIG. 14B, a non-reference pattern P2 matching the
inclination S of +2 connects with the reference pattern P1 in a straight
line. So, the inclination S of the nozzle array L can be determined to be
"+2". In this example, since the resolution of these patterns in the main
scan direction is 1,200 dpi, the nozzle array L with the inclination of
"+2" has an inclination S in FIG. 12 of about 42 μm. If it is decided
from the printed vertical line pattern that the inclination is
approximately median between "+2" and "+4", a median value of "+3" may
betaken as the inclination S. In this example, the inclination S can be
acquired in units of 2,400 dpi. Therefore, the patterns shown in FIG. 14A
and FIG. 14B are third patterns used to acquire the inclination of a
nozzle array. To print the third patterns, the head unit functions as a
third pattern printing unit under the control of the print control unit
500.

[0090] The inclination S of the n-th nozzle array acquired in step S14 of
FIG. 11 is stored in a predetermined region (third storage portion) in
the ROM 402. Here, first to fourth nozzle array (n=1 to n=4) are taken as
nozzle arrays K, C, M, Y with inclinations of S(K), S(C), S(M), S(Y),
respectively. So, the inclination detection unit includes a third pattern
printing unit and an input unit for entering an amount of shift
(equivalent to the inclination S). It is noted, however, that the
inclination detection unit does not have to include the third pattern
printing unit. For example, the surface of the print head in which the
nozzle arrays are formed may be detected by an optical sensor to
determine the inclination of the nozzle array.

[0091] The patterns P1, P2 are just an example and, to enhance the
detection accuracy of the inclination, the resolution may further be
increased. To widen the detection range of inclination, the horizontal
size of the patterns may be expanded and the number of different
non-reference patterns P2 increased. Further, to raise the level of
recognizability of the vertical line patterns made up of patterns P1, P2,
the vertical size of the patterns P1, P2 may be extended to elongate the
vertical line or the width of the vertical line increased to more than
two dots.

[0092] If the number of nozzles used in the nozzle array is fewer than
256, the patterns P1, P2 may be required to be changed according to a
variety of printing conditions, such as reducing the vertical size of the
patterns P1, P2. It is also possible to acquire the inclination S by
printing seven different non-reference patterns P2 along with seven
reference patterns P1 in a one-to-one relation, taking density
measurements of the printed patterns and determining the inclination S
from the result of measurements. In that case, the patterns PA, PB, such
as shown in FIG. 9, may be printed as the patterns P1, P2.

[0093] Next, from the inclination S of the n-th nozzle array L thus
obtained, the positions of the nozzles to be used in the nozzle array L
are acquired and, from these positions, an inclination coefficient k is
determined (step S15). The inclination coefficient k corresponds to the
print position shift or deviation resulting from the inclination of the
nozzle array L. The print control unit 500 functions as a first
calculation unit to determine the inclination coefficient k. Further,
from the inclination coefficient k, a correction value B for adjusting
the print position deviation resulting from the inclination of the nozzle
array L is calculated (step S16). The method of calculating the
correction value B will be explained as follows.

[0094] In the example of FIG. 12, the nozzles NA to be used in the nozzle
array L are a group of nozzles ranging from nozzle number A1 to nozzle
number A2. The nozzles NA to be used differ depending on the print mode.
In the nozzle array L made up of a total of 1,200 nozzles, the lowermost
nozzle NB is assigned a nozzle number 0 and the uppermost nozzle NT a
nozzle number 1199. The nozzle numbers from A1 to A2 have a relation of
A1<A2.

[0095] The inclination coefficient k is calculated from an equation (1)
shown below. Here N represents the total number of nozzles in the nozzle
array L and in this case N=1,200.

k=[{(A2-A1)/2}+A1-{(N-1)/2}]/{(N-1)/2} (1)

From this inclination coefficient k and inclination S, the correction
value B is determined by an equation (2) shown below.

B=k×(S/2) (2)

The correction value B corresponds to a distance between a position X(A)
on the axis Ox, which represents a middle point of the group of nozzles
NA to be used projected onto the axis Ox, and the origin of the axis Ox.
The print control unit 500 functions as a second calculation unit to
determine the correction value B.

[0096] Next, the correction value B will be explained by referring to FIG.
6C.

[0097]FIG. 6C is an enlarged view showing a positional relation between
lines (L(C) and L(M)) in FIG. 6B printed with a cyan ink and a magenta
ink, respectively. In FIG. 6C, the center lines O(C), O(M) of the printed
lines L(C), L(M) do not match the misregistration adjustment position P
associated with the nozzle arrays C and M. The reason for this
misalignment is that, in addition to the nozzle arrays C, M having their
own inclinations, the nozzles to be used are deviated from the center
line of each nozzle array and situated near one of its sides. In such a
case, to align the center lines O(C) and O(M) of the printed lines L(C)
and L(M) requires a correction operation of shifting the positions of the
center lines O(C), O(M) to the misregistration adjustment position P, as
shown by the arrows in FIG. 6C. The amounts of position correction for
the center lines O(C), O(M) correspond to the correction values B (C),
B(M) for the nozzle arrays C, M, respectively.

[0098] Then, by repetitively executing the processing from step S13 to
step 16 on all nozzle arrays K, C, M, Y, the correction values B for the
nozzle arrays are calculated (step S17). The correction value B for a
nozzle array with no inclination is 0 (B=0).

Next, from the print position adjustment values (misregistration
adjustment values) for high-speed mode V1(C), V1(M), V1(Y) described
above, adjustment values (misregistration adjustment values) for
high-quality mode V2(C), V2(M), V2(Y) are calculated (step S19). That is,
print position adjustment values V2(C), V2(M), V2(Y) for nozzle arrays C,
M, Y with respect to the reference nozzle array K are calculated by
equations (6), (7), (8) shown below. These adjustment values are
correction values that take into account the inclinations of the nozzle
arrays (print head inclination) and the positions of nozzles to be used.

V2(C)=V1(C)-C(C) (6)

V2(M)=V1(M)-C(M) (7)

V2(Y)=V1(Y)-C(Y) (8)

The adjustment values V2(C), V2(M), V2(Y) thus obtained are stored in a
storage medium as adjustment values V2 for high-quality mode (step S20).
Adjusting the print positions of the nozzle arrays C, M, Y with respect
to that of the nozzle array K in the high-quality mode by using the
adjustment values V2(C), V2(M), V2(Y) allows high-quality images with
reduced color deviations to be printed.

[0100] In the above explanation, the inclinations S of nozzle arrays are
determined from test patterns and, based on the inclinations, the
correction values B are calculated.

[0101] The method of determining the correction value B is not limited to
this one. Since the correction value B is equivalent to the distance
between the position X(A) and the origin of axis Ox, the correction value
B can also be acquired by directly calculating the distance between the
position X(A) and the origin of axis Ox. This may be achieved as follows.
The reference pattern P1 (see FIG. 13) is formed by a nozzle situated at
the center of the entire nozzle array and then the non-reference pattern
P2 of FIG. 13 is formed by a nozzle situated at the center of the range
of nozzles NA to be used. Then, a printed pattern in which the reference
pattern P1 and the non-reference pattern P2 are connected in a straight
line is selected, allowing the distance between the position X(A) and the
origin of axis Ox to be determined directly. Therefore, the head unit and
the print control means, both used to print the aforementioned patterns,
and the input unit for entering the pattern printed result together
constitute a third acquisition unit. It is noted, however, that printing
the test patterns using the uppermost nozzle NT and the lowermost nozzle
NB, as in the method of the second embodiment, makes a pattern
misalignment in the main scan direction more distinctive, allowing the
correction value B to be determined with an improved precision.

Other Embodiments

[0102] The number and kinds of inks used to print images, the order of
applying a plurality of inks and the kinds of print modes are not limited
to those of the embodiments described above but can be chosen
arbitrarily. This invention can widely be applied to a variety of print
modes activating different numbers of nozzles at different positions. The
print modes may include one that uses all nozzles in a nozzle array and
one that uses only a part of them. This invention can also be applied to
a construction in which a plurality of print heads are arranged in line
in the sub-scan direction so that the nozzle arrays formed in these print
heads are connected end-to-end in the sub-scan direction. In that case,
those connected nozzle arrays stretching in the sub-scan direction are
taken as an extended nozzle array and a plurality of such extended nozzle
arrays may be used, one for each of different inks. As with the preceding
embodiments, in a plurality of print modes that activate nozzles at
different positions in each extended nozzle array, the print position of
each extended nozzle array can be adjusted by taking into consideration
an inclination of each extended nozzle array (or inclination of the print
head). The inclination of the extended nozzle array includes an
inclination of at least one of a plurality of print heads making up the
extended nozzle array.

[0103] The print head is not limited to an ink jet print head with ink
ejecting nozzles as printing elements and may also include a print head
having a variety of kinds of printing elements capable of applying ink to
a print medium.

[0104] This invention is applicable to all devices that use print media
including paper, cloth, leather, unwoven fabric and even metal. The
applicable devices include office equipment such as printers, copying
machines and facsimiles and industrial manufacturing machines. Further,
this invention is particularly effectively applied to devices that print
on large-size print media at high speed.

[0105] While the present invention has been described with reference to
exemplary, embodiments, it is to be understood that the invention is not
limited to the disclosed exemplary embodiments. The scope of the
following claims is to be accorded the broadest interpretation so as to
encompass all such modifications and equivalent structures and functions.

[0106] This application claims the benefit of Japanese Patent Application
No. 2010-019162, filed Jan. 29, 2010, which is hereby incorporated by
reference herein in its entirety.